1. Field of the Invention
The present invention relates to a via structure having an open stub and a printed circuit board having the same, and more particularly, to a via structure having an open stub that has an open stub connected to a via pad, and a printed circuit board having the same.
2. Description of the Related Art
As the transmission rate of mobile devices such as PCs, mobile phones, and tablet PCs and the data rate increase, the amount of data transmitted through a circuit board and the usable frequency are also increasing.
Conventional signal transmission via in a substrate and circuit board have a structure in which a via passing through an insulating layer is connected between a first transmission line for receiving a signal and a second transmission line for outputting a signal through a via pad.
The longer the line and the higher the frequency, the greater the transmission loss value of a signal transmission channel of the circuit board having the conventional via and via pad, and return loss characteristics are also deteriorated due to specific impedance discontinuity occurring in the via and so on.
The characteristics of the conventional signal transmission channel will be described with reference to FIGS. 7 and 8.
FIG. 7 is a view showing a signal transmission channel equivalent circuit in the conventional via structure and circuit board, and FIG. 8 is a graph showing signal transmission channel characteristics in the conventional via structure and circuit board in accordance with FIG. 7.
FIG. 7 is a channel equivalent circuit of the conventional via pad structure, and a resistor R1 and L1 between transmission lines represent equivalent resistance and inductance of the via. In the via having the conventional via pad, since a capacitance between a top via pad without an open stub and a ground plane and a capacitance between the top via pad and an inner layer upper via pad are negligibly low, they can be omitted from the equivalent circuit, and a capacitance between a bottom via pad and the ground plane and a capacitance between an inner layer lower via pad and the bottom via pad are the same. In the signal transmission channel having the conventional via pad, as shown in FIG. 8, as the frequency increases, the loss increases and the return loss characteristics are deteriorated.